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43
Microdiscectomy
David Lee Spencer and Avi J. Bernstein
Goals of Surgical Treatment
Microdiscectomy allows the surgeon to perform all of the maneuvers of the
routine hemilaminotomy and discectomy procedure with the aid of improved illumination and magnification. Table 43–1 is a list of favored instruments. Familiarity with draping, positioning, and adjusting the operating microscope is necessary before the surgeon attempts to perform the
procedure. The use of operating loupes and a head lamp is a viable alternative to the operating microscope; however, the operating microscope has
distinct advantages.
Indications for Surgery
1. Radicular signs and symptoms of nerve root compression due to a disc
herniation.
2. Unresponsive or inadequately responsive to symptomatic nonopera-
tive treatment.
3. The offending disc herniation with nerve root compression must be
demonstrated on a magnetic resonance imaging (MRI) scan, a computed tomography (CT) scan, or a myelogram.
Contraindications
1. Inconclusive diagnosis of herniated nucleus pulposus (HNP)
2. Symptom amplification
Advantages
1. Allows the surgeon to perform the procedure with greater accuracy
and with less risk of complications due to the surgical misadventures
of excessive bleeding, nerve root damage, dural lacerations, and
missed and retained disc fragments.
2. The postoperative course is so predictable and benign that the surgeon
can confidentially release the patient from the hospital the day of
surgery, making this truly an outpatient surgical procedure.
3. Relatively few instruments are required for the procedure.
Procedure
The description of the technique that follows is a step-by-step guide that
applies to the routine disc herniation (Fig. 43–1). The following special situations require deviations from the standard technique and are described
separately:
Table 43−1. Preferred Instruments for Microdiscectomy Surgery
McCullough retractor set
Frazier suction tip, No. 4 or No. 12
Love 90-degree nerve root retractor
Criles small-narrow 90-degree Love nerve root retractor
Mallis bipolar forceps
Extra-long 90-degree Love nerve root retractor
30-cc syringe
Standard Freer elevator
Small Freer elevator
Laryngeal cannula
Nerve hook
Caspar hooks-short tip, medium tip, and long tip
Caspar grasping pituitary rongeur, 12 × 3 mm
Cushing rongeur str., 7씵,3mm
Cushing rongeur str., 5씵,3mm
Cushing rongeur up-biting, 5씵,3mm
Kerrison rongeur, 7.5씵, 40 degrees, 3 mm
Kerrison rongeur, 7.5씵, 40 degrees, 1 mm
Kerrison rongeur, 40 degrees, emm x-long shaft
Cobb spinal elevator, 11씵
Cobb spinal curet, No. 4
Knife handle, No. 3
Knife handle, No. 7
Short tissue forceps with teeth
Adson tissue forceps
Straight Mayo
Needle holder, 5씵
1. Foraminal herniation
2. Far lateral herniation
3. Completely extruded fragment
4. Recurrent herniation
The surgery is usually performed with the patient in a prone position
under general anesthesia. It is possible to use spinal, epidural, or local anesthesia; however, the benefits are not worth the added complexity and the
occasional unpredictability of these regional anesthetic techniques. The
patient is placed prone on any operating frame that allows abdominal
decompression and flexion of the lumbar spine. The Wilson frame is the
simplest, most readily available frame that meets these two criteria. The
surgeon usually operates from the side of the disc herniation with the microscope positioned at the head of the table on the opposite side.
When the patient is anesthetized and positioned prone on the Wilson
frame, in maximum flexion, the back is prepped and draped in routine
fashion. A spinal needle is placed into the back at a location presumed to
be the level of the disc herniation, and a lateral x-ray is taken to identify the
exact surface location for the incision over the disc herniation. The opportunity to misinterpret the localizing x-ray, especially with nonstandard
anatomy or obesity, must not be underestimated. Surgically exposing the
wrong level is one of the most common surgical misadventures. When necessary, repeat x-rays must be taken, not only initially but also during the
procedure to document absolutely the appropriate location of the surgical
exposure. The skin incision size depends on the obesity of the patient; the
more obese the patient, the larger the incision must be to allow access in
the depths of the wound. Generally speaking, the incision is 1 to 2 inches
in length. The size of the skin incision, however, is the least relevant aspect
of the surgical procedure. It has never been reported that favorable results
of discectomy surgery correlate with the length of the skin incision. The
skin incision is in the midline; however, the fascial incision is made just
lateral to the spinous processes, preserving the supraspinous and interspinous ligaments. Maintaining the interspinous and supraspinous ligaments is important to provide countertraction for the microdiscectomy retractor. With a Cobb elevator and digital dissection, the appropriate interlaminar space is exposed, palpated, and the facet identified. The microdiscectomy retractor is inserted. There are several retractors on the market
that are adequate. The McCullough retractor with its blades of variable
width and length is an excellent retractor system for this surgical procedure.
After insertion of the microdiscectomy retractor, the previously
sterilely draped operating scope is brought into the field for the remainder
of the procedure. The operating scope optimal for the microdiscectomy
procedure must have a stand that is high enough to provide enough elevation to clear the patient’s back on the Wilson frame and focus in the depths
of the wound with at least a 300-mm focal length objective lens. The focal
length of the objective lens determines the space between the microscope
and the surface of the back. Objective lenses of less than 300 mm do not
provide enough space between the microscope and the back to perform
surgery. Lenses over 350 mm are so far away from the back that the surgery
can be awkward. The optimal focal length objective lenses depending on
the size of the patient is 300 to 350 mm. The microscope head must also be
adjustable in all planes with a universal joint. The surgeon must be able to
angle the microscope head when necessary in every direction to obtain appropriate visualization. The initial view through the microscope of the
operative field is frequently a confusing array of fat, muscle strands, and
bleeding. Muscle and fat debris must be removed with a pituitary rongeur
and bleeding controlled with electrocautery. Meticulous hemostasis is
mandatory when performing this procedure. The facet joint is the most
readily identifiable local anatomic landmark and is the key to surgical exposure. The inferior medial margin of the facet joint must always be identified. This is most expeditiously done by removing the falciform flavum
and the inferior medial facet capsule with a 3-mm, 40-degree Kerrison
rongeur. Except at the LS-S1 level, it is always necessary to perform a partial medial facetectomy of both the inferior and the superior facet. The use
of a high-speed drill bur is frequently recommended for this bone removal;
however,it is not necessary and invites excessive and unnecessary bone removal. The 3-mm, 40-degree Kerrison rongeur is the only instrument necessary for bone and ligamentum flavum removal.
After identifying the facet joint, the 40-degree rongeur is insinuated
into the facet joint, and the inferior medial margin of the inferior facet can
be removed in a piecemeal fashion, exposing the medial margin of the su-
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200
SECTION III THE LUMBAR SPINE
Eurostile
Disc
Annulus
Spinal
nerve root
A
Figure 43–1
(A) Axial computed tomography (CT) scan demonstrating left-sided disc herniation. (B) Diagrammatic representation of lumbar disc herniation.
Nerve root
compression
B
Eurostile
43 MICRODISCECTOMY
201
■
JC
Disc
capsule
Deliver disc
fragment
in one piece
Nerve hook
(nerve retractor)
Mobilize
nerve
root
medially
LF
Figure 43–3
Proximally extruded disc herniation.
Figure 43–2
Laterally placed hemilaminotomy allows retraction of nerve root and disc hernia-
tion removal without even visualizing the dural sac.
Figure 43–4
Foraminal disc herniation.
Figure 43–5
Far lateral extraforaminal disc herniation.
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202
SECTION III THE LUMBAR SPINE
Eurostile
perior facet. It is readily identifiable by the glistening articular facet surface. The exact interface between the ligamentum flavum where it attaches
to the superior lateral margin of the superior lamina is identified by mobilizing the ligamentum flavum with a medium-sized curet. This exposes the
exact inferior and lateral margin of the ligamentum flavum. The recommended surgical entry into the spinal canal is always at this point. Having
identified the exact margin between the ligamentum flavum and its attachment to the superior lamina, the 3-mm, 40-degree Kerrison rongeur is carefully insinuated into the spinal canal underneath this bony margin. The
laminotomy can then be performed by removing as much ligamentum
flavum as necessary superiorly and medially, and bone laterally, superiorly, and inferiorly. Just how much bone and or ligamentum flavum is removed depends on the local anatomy and the location of the disc fragments to be removed. For example, an inferiorly extruded disc may require
virtually no superior medial ligament removal but extensive inferior bone
removal to allow access to the fragment that is opposite the pedicle. The
laminotomy should be situated lateral enough in the canal to provide
direct exposure of the nerve root without any overhanging lateral bone.
The main dural sac may never actually be visualized medial to the nerve
root through the laminotomy exposure (Fig. 43–2). This lateral positioning
of the laminotomy helps to prevent inadvertent dural lacerations and
nerve root injury from overretraction. Once the laminotomy has been performed, it is imperative to identify the nerve root.
Dissection through the epidural fat with bipolar forceps and coagulation of veins with bipolar cautery is frequently necessary. Whenever there
is difficulty identifying or locating the nerve root, it is always helpful to
identify the pedicle. Identifying the pedicle by palpation with a nerve hook
will always lead one to the appropriate location of the nerve root. If the
nerve root is not properly exposed, the laminotomy needs to be expanded
by more bone removal laterally or superiorly to safely identify the nerve
root. Medial mobilization of the nerve root off of the disc herniation is
sometimes very difficult. The nerve root is frequently stretched tautly over
a disc herniation making it difficult to even identify the interface between
the nerve root and the disc, much less to mobilize and retract the nerve root
without potential nerve root damage. The Adson blunt nerve hook is an
ideal tool for mobilizing the nerve root. It is always safest to mobilize the
nerve root from the caudal to cephalad direction in the line of the nerve
root rather than from lateral to medial.
Identify the nerve root caudal to the point of impingement from the disc
herniation. This location allows easy identification of the ventral surface
of the nerve root. Working cephalad underneath the nerve root with an
Adson blunt nerve hook, the nerve root can be mobilized off of the disc
herniation without risk of penetrating the nerve root or damaging it. On the
other hand, trying to dissect the nerve root off of the disc herniation at the
point of contact by working from lateral to medial may injure the nerve root
because of the poor demarcation between the nerve root and disc herniation and the local adhesions. It is also frequently advisable to insert the
Love nerve root retractor underneath the nerve root caudal to the disc
herniation and then gradually work the nerve root retractor cephalad. This
also is a safe way of mobilizing the nerve root with less risk of nerve damage. Of the various nerve root retractors available, the right-angle Love
nerve root retractor is optimal because the retractor is not sticking straight
up toward the microscope interfering with vision and with the operating
surgeon.
Preventing and controlling bleeding is one of the key aspects of an expeditious and safely performed discectomy operation. Bipolar cautery of
epidural veins is mandatory. The epidural veins are frequently strapped
over the disc herniation and are exsanguinated and are not necessarily ob-
vious. Incision of these exsanguinated veins can result in an unexpected
and annoying rush of venous blood. To prevent this, carefully scrape the
surface of the disc herniation with the bipolar forceps, cauterizing these
exsanguinated veins prior to incising the disc herniation. This will usually
prevent the annoying bleeding that can otherwise occur with the incision
of the capsule of the disc herniation. If for some reason there is continued
annoying bleeding, the spinal canal can be carefully packed with small
thrombin-soaked Gelfoam pledgets and cottonoid patties above and below
the disc herniation to control the bleeding during the discectomy procedure.
After incising the capsule of the disc herniation, it is helpful to mobilize
the fragment of the disc with a variety of nerve hooks prior to extraction.
This improves the likelihood of delivering the fragment in one piece rather
than breaking the fragment and removing it in a piecemeal fashion. Decker
and pituitary rongeurs are necessary for fragment removal. Once the fragment is removed from the spinal canal, the disc space itself is debrided of
loose disc material with a variety of pituitary and Decker rongeurs. It is
usually necessary to enlarge the annular rent caused by the disc herniation
to allow adequate debridement of the disc space. When necessary, the
overhanging lip of the posterior vertebral body, which makes entry into the
disc space difficult, can be partially removed with a 3-mm, 40-degree Kerrison rongeur, facilitating disc space debridement. Forceful irrigation of
the disc space helps to mobilize unrecognized hidden intradiscal fragments and facilitate their removal. Simple debridement of the disc space
with Decker and pituitary rongeurs and a ring curet and nerve hooks cannot be relied on to identify all loose intradiscal fragments. Forceful irrigation with a 30-cc syringe and a laryngeal cannula may mobilize and identify a previously unrecognized fragment. Using an antibiotic saline mixture also is an effective means of delivering interoperative antibiotics to the
relatively avascular disc space, thereby, it is hoped, reducing the risk of
discitis. The goal of disc space debridement in this operation is not to remove as much disc material as possible but to identify those loose or partially loose intradiscal fragments that may result in a recurrent disc herniation at some later date. Intradiscal irrigation will flush loose fragments out
of the disc into the laminotomy site. If the fluid disappears, there must be
an anterior perforation of the disc with possible damage to retroperitoneal
structures.
When no further loose disc fragments are retrievable from the disc
space or the epidural space, all cottonoid patties and Gelfoam pledgets that
may have been used for hemostasis are removed. Additional coagulation of
epidural veins is performed if necessary. The dura is inspected for tears
and spinal fluid leakage and the nerve root is inspected for any residual
compression from either unrecognized disc fragments or bony stenosis.
The lateral recess is routinely decompressed in this surgical procedure by
virtue of the removal of the medial bony lip of the superior facet with the 3mm, 40-degree Kerrison rongeur in the process of performing the
laminotomy. The disc space and the epidural space can be irrigated with a
dilute solution of Marcaine (0.125%) for postoperative analgesia. Duramorph may also be locally applied to the nerve root prior to closure. The
skin and subcutaneous tissue are locally infiltrated with Marcaine for postoperative analgesia. Ten milligrams of Decadron IV push in the recovery
room is helpful for management of postoperative pain.
The generic technical description outlined above applies to the disc
herniation in the routine location (Fig. 43–1) and emphasizes the following
important points:
1. Absolutely accurate determination of the correct level.
2. Lateral placement of the laminotomy to minimize risk of dural tears
and nerve root injury by overretraction and manipulation.
3. Minimize bleeding by identifying and bipolar coagulating veins before
they are severed and bleed.
4. Aggressive irrigation of the disc space to mobilize hidden and
sequestered disc fragments that may result in a recurrent disc herniation if not recognized and removed.
Special Situations
Extruded Disc
When the herniated disc fragment is completely extruded and migrated
away from the disc space, it is a special situation. It is not necessary or
advisable to expose the disc space and enter and debride it as is routinely
required when the disc herniation is in continuity with the disc space. For
example, for a fragment migrated proximally from the L4–5 disc space residing opposite the L4 pedicle with L4 nerve root compression (Fig. 43–3),
the surgical approach should be at the L3–4 interspace, not the L4–5 disc
level. The level of surgical exposure is based on where the disc fragment is
at the time of surgery, not where it originally came from. Entering the spinal canal at L3–4 at the level of the inferior lateral margin of the ligamentum flavum as described above is exactly at the level of the L4 pedicle. Extending the laminotomy caudally by removing portions of the superior
lateral lamina of L4 provides excellent exposure of the disc herniation
without any removal of facet joint or ligamentum flavum. The proximally
migrated fragment is always medial to the nerve root, and therefore the
laminotomy needs to be extended caudally and medially enough to allow
retrieval of the disc herniation medial to the nerve root through the socalled axillary approach. There is no need to enter the L4–5 disc space
when the herniated fragment has completely extruded from the disc space
and has migrated away from the disc.
Foraminal disc herniations (Fig. 43–4) are a second special situation
that can be especially difficult to access, and they require significant bone
and facet removal. In these cases it is optimal for the surgeon to stand opposite the disc herniation to facilitate working under the facet in the foramen for disc herniation removal. Significant bone must be removed from
both the inferior and superior facet to expose the exiting nerve root and
identify and retrieve the herniated fragment. It is not at all uncommon for
very small fragments to migrate into the foramen causing severe symptoms. An exhaustive search under and behind the nerve root under the
Eurostile
43 MICRODISCECTOMY
203
■
pedicle with nerve hooks must be performed to avoid missing these small
hard-to-find fragments. The fragments are frequently not continuous with
the disc space, and therefore simple debridement of the disc space in the
foramen does not lead to identification and removal of the fragment.
Foraminal disc herniations in general are the most difficult fragments to
identify and remove. This is largely a result of the surgeon’s desire to limit
the exposure as much as possible by removing as little of the facets as necessary. Despite this desire to maintain the facets, it is very often necessary
to remove a very large portion of both the superior and the inferior facet.
Lateral extraforaminal disc herniations are another special situation
(Fig. 43–5). The most direct access to a far lateral disc herniation is through
a paramedian muscle splitting approach. The skin incision is made two
fingerbreadths lateral to the midline and opposite the disc herniation and
carried down through the intermuscular septum by blunt dissection. The
same microdiscectomy retractors that are used for a routine microdiscectomy procedure are used here too, as is the operating microscope.
The transverse process of the vertebral body just proximal to the disc
herniation is identified. The inferior medial margin of the transverse
process where it blends with the pars interarticularis is the critical angle to
identify. The intertransverse membrane is incised along this margin of the
transverse process. The 3-mm, 40-degree Kerrison rongeur is then used to
remove a very small portion of the medial inferior transverse process margin. The rongeur can also be used for bony removal of a small portion of the
lateral aspect of the facet to facilitate exposure. Careful dissection underneath the base of the transverse process results in identification of the
nerve root. Arterial and venous vessels in this location need to be meticulously identified and coagulated to prevent excessive bleeding. Dissection
medial to the identified nerve root provides access to the lateral margin of
the disc. With careful lateral mobilization of the nerve root, the disc fragments should be identifiable and mobilizable with nerve hooks. Retrieval
of the disc fragment results in decompression of the nerve root. The disc
space itself can be minimally debrided through this approach when necessary with a Decker and pituitary rongeurs.
Repeat microdiscectomy surgery at the site of previous surgery is also a
special situation. Scar tissue can make it difficult to identify the normal anatomic landmarks and in some cases, the bony landmarks have been removed in the original operation. The interlaminar space is exposed once
again with a Cobb elevator by identifying the superior lateral margins of
the inferior spinous process. The dissection is carried down to the lamina
subperiosteally. These bony landmarks will allow the dissection to then
proceed cephalad, exposing the facet joint and the lateral margin of the
previous laminectomy defect. Being absolutely certain where the bony
margin of the previous laminectomy defect is will help prevent inadvertent dural lacerations and nerve root injuries. A large curet can also be
helpful in dissecting the dense scar tissue off of the bony margin. In
general, the larger the instrument used, the less the likelihood of inadvertently penetrating scar tissue and dura. After definitively identifying the
facet joint, the 3-mm, 40-degree Kerrison is insinuated into the facet joint
and a partial medial facetectomy of the inferior facet is performed. This
helps to clearly expose the medial aspect of the superior facet and the
lateral margin of the previous laminectomy defect. The rongeur can then be
safely insinuated into the spinal canal at the inferior lateral margin of the
laminotomy defect. Additional bone is removed inferiorly, laterally, and
superiorly as needed for access to the spinal canal. The amount of spinal
canal access at the level of the pedicle is limited by the pedicle and cannot
extend laterally beyond the medial margin of the pedicle. This can provide
very limited exposure in the face of dense intraspinal adhesions. Further
access to the spinal canal can always be achieved proximal to the pedicle
by removing bone superior and lateral to the medial margin of the pedicle
with a 40-degree Kerrison rongeur. Most recurrent disc herniations do not
migrate away from the disc space due to epidural scar tissue. Accessing the
disc space superior to the pedicle and lateral to the scar tissue encompassing the dura and the nerve root is an excellent way to avoid inadvertent
damage to the nerve root and dura that is obscured by the scar tissue. It is
frequently impossible to identify the nerve root and dura in the encased
scar tissue. It is not advisable to attempt sharp dissection of the scar tissue
to identify the dura and the nerve root. Without direct visualization of the
nerve root and/or the dura, the disc space is entered lateral to the herniation superior to the pedicle and lateral to the dura and the nerve root.
Once the disc space is entered, using pituitary and Decker rongeurs the
disc space can be aggressively debrided and the herniated fragments mobilized, retrieved, and removed without ever visualizing the dura and the
nerve root. Exploration of the disc space with variable-length nerve hooks
and forcible irrigation with antibiotics irrigation are absolutely mandatory
when retrieving these herniated discs from the unseen recesses of the
epidural space underneath the scar tissue encasing the dura and the nerve
root. In this fashion, repeat microdiscectomy surgery can be performed
without disrupting the dura and the nerve root and the encasing scar
tissue. This not only significantly reduces the risk of nerve root and dura
injury at the time of surgery but also reduces the probability that additional
scar tissue will form around the dura and the nerve root. Repeat microdiscectomies performed in this fashion do not necessarily produce any increased scar tissue around the dura and the nerve root at the location of the
recurrent disc herniation.
In summary, the special situations identified include the disc fragment
migrated cephalad away from the disc space, the foraminal disc herniation, the lateral extraforaminal disc herniation, and finally the recurrent
disc herniation at the site of previous surgery. These special situations
demand slightly modified surgical techniques compared to the routine
disc herniation.
Postoperative Care
Postoperative management usually requires no organized therapeutic regimen. Rapid return to activities of daily living, including light to sedentary
work beginning within the first postoperative week, is the standard. Walking is therapeutic in an attempt to maintain mobility of the nerve roots
postoperatively and minimize scarring. Gradual increase in physical activities of bending, lifting, and twisting usually allows the individual to resume full, unrestricted activities at 4 to 8 weeks following surgery. Patients
on workers‘ compensation always request and require longer recovery
times before returning to work, partly because of the genuine desire to prevent reinjury and partly because they enjoy the extended paid vacation.
Postoperative activity status, rehabilitation, and work restrictions do not
correlate with any increased or decreased incidence of recurrent disc
herniations.
Pitfalls
Failure to achieve the expected pain relief that should occur in at least 90%
of patients is due to a variety of causes. Not removing any or all of the disc
herniation for whatever reason is the most obvious but the least frequent
cause of failure. Most commonly, the patient has preoperatively a variety of
symptoms including back pain and leg pain and an abnormality on an imaging study that is interpreted as a disc herniation but in fact is not causing
symptomatic nerve root compression. Removing an asymptomatic disc
herniation that is not producing any nerve root compression cannot be expected to improve the patient’s clinical condition. It is also well recognized
that patients with secondary gain continue to complain of pain postoperatively. Perineural and peridural scar tissue is always a suspected culprit in
persistent postoperative pain. Despite the intuitive appeal of scar tissue as
being an explanation for persistent postoperative pain, it is not a proven
fact that scar tissue alone results in significant symptoms following a
simple uncomplicated microdiscectomy procedure. On the other hand,
dense perineural scar tissue certainly makes reoperation more difficult.
Scar tissue also may tether the nerve root, making it more vulnerable to
compression than it otherwise would be.
In conclusion, with the benefit of preoperative pinpoint localization of
a disc herniation with a CT scan or an MRI scan, microdiscectomy surgery
as described can routinely be performed on an outpatient basis with a
safety and efficacy rate that exceeds 90%. Microdiscectomy surgery is currently the gold standard for the surgical treatment of an individual with
sciatic pain due to a disc herniation unresponsive to symptomatic treatment.
Suggested Readings
Bosacco SJ, Berman AT, Bosacco DN, Levenberg RJ. Results of lumbar disk
surgery in a city compensation population. Orthopedics 1995;18:351–
355.
Cuckler JM, Bernini PA, Wiesel SW, Booth RE Jr, Rothman RH, Pickens GT.
The use of epidural steroids in the treatment of lumbar radicular pain:
a prospective, randomized, double-blind study. J Bone Joint Surg Am
1985;67:63–66.
Hudgins WR. The role of microdiscectomy. Orthop Clin North Am
1983;14:589–603.
Spencer DL, Bernstein AJ. Lumbar intervertebral disc surgery. In: Bridwell
K, DeWald R, eds. The Textbook of Spinal Surgery. 2nd ed. Philadelphia: Lippincott-Raven; 1997:1547.
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SECTION III THE LUMBAR SPINE
Eurostile
44
Far Lateral Discectomy
Kurt W. Von Rueden and Laura B. Flawn
Goals of Surgical Treatment
Relief of radicular pain secondary to disc herniation lateral to the intravertebral foramen.
Diagnosis
Far lateral or extraforaminal herniated nucleus pulposus (HNP) are disc
herniations lateral to the neuroforamen in the exit or far lateral zones. Ian
McNab referred to this area as the hidden zone, as it is hidden from myelography.Prior to the advent of computed axial tomography (CAT) scans and
magnetic resonance imaging (MRI), these lesions were often missed. Extraforaminal disc herniations compress the exiting nerve root or dorsal root
ganglion superiorly into the pedicle above. The nerve root is less mobile in
this area, and its ability to migrate away from disc herniations is less than
that of intercanal HNPs. The dorsal root ganglion (DRG) is variable in size
and location with respect to the neuroforamen. The DRG is largest in the L5
and S1 levels, being 5 to 6 mm wide and 11 to 13 mm long.
Incidence
Of 150 consecutive disc herniations in our practice, 15 were lateral extraforaminal HNPs. In the literature the incidence is reported at 1 to 11%.
Imaging
CAT, MRI, or discogram CAT.
1. MRI—noninvasive (Fig. 44–1).
2. Sagittal images at pedicle level and lateral can reveal lesion (Fig. 44–2).
3. Discogram CAT (Fig. 44–3) confirms that disc herniation is contiguous
with disc space.
4. Diagnostic blocks: extraforaminal nerve root block can confirm diagnosis. Addition of steroids may be therapeutic.
7. Narrow-bladed retractors with a variety of depths to facilitate the exposure. Anterior cervical discectomy retractor systems with various interchangable blades are readily available in most operating rooms and
work well.
8. Identify and remove the intertransverse ligament from superior medial
to inferior lateral along the course of the exiting nerve root.
9. The exposure is in the axilla of the exiting nerve root.
10. Partial resection of the lateral facet joint can facilitate exposure of the
disc (Fig. 44–5B).
11. Often the free fragment presents itself after removal of the intertransverse ligament.
12. The discs can be entered through the hole created by the herniation
and additional fragments removed as indicated (Fig. 44–3).
13. A reverse foraminotomy is done to remove any foraminal bony spurs or
other causes of neural impingement.
14. After decompression the nerve root is covered with fat graft soaked in
Depro-Medrol and the wound is closed in layers.
Exposure Secrets
1. The interval between the multifidus and longissimus is subtle but definable (find the interval, don’t create one).
2. When working around the intertransverse ligament or anterior to it, always use bipolar cautery to avoid thermal injury to the nerveor the DRG.
3. Resection of the intertransverse ligament should proceed along the
course of the nerve root from a superior medial to an inferior lateral
direction to avoid cutting across the nerve root.
4. Meticulous dissection facilitates the approach and cannot be overemphasized.
5. Any bleeding can significantly obscure the view.
Differential Diagnosis
1. Enlarged ganglia
2. Conjoined nerve roots
3. Nerve root tumors
Presentation
1. Severe radicular pain.
2. May involve nerve roots.
3. L4-L5 most common level (L4 radiculopathy).
4. SLR may be negative; check femoral stretch test.
5. Failure of standard laminotomy to relieve symptoms (wrong level,
wrong location at right level.
Indications for Surgery
1. Same as with intracanal HNPs
2. Failed nonoperative management
3. Radicular pain corresponding to the lesion documented on confirmatory imaging studies
4. Progressive weakness
Contraindications to Lateral Approach
Majority of herniation is medial to the pedicle.
Advantages of Lateral Approach
1. Direct visualization of pathology.
2. Postoperative instability minimized with preservation of pars interarticularis and the inferior facet joint.
3. Simultaneous laminotomy, and extraforaminal approach is possible if
indicated.
Procedure
1. Headlight illumination and loupe magnification or microscope is recommended.
2. Midline skin incision (Fig. 44–4A).
3. Fascial incision 1 to 2 cm lateral.
4. Locate the interval between multifidus and longissimus muscles (do
not create an interval).
5. Identify facet joint above and below the level of pathology; intraoperative x-ray confirms level (Fig. 44–4B).
6. Expose transverse processes above and below as in approach for posterior lateral spinal fusion surgery (Fig. 44–5A).
Pitfalls
1. Overmanipulation of the DRG can cause mechanical injury.
2. Thermal injury can result from use of cautery. Surgicel, Gelfoam with
thrombin, or bipolar cautery should be used any time the surgeon is
working near the nerve root.
3. Operating on the wrong level is prevented by understanding the anatomy and obtaining intraoperative x-rays as necessary. If you don’t find
what you think should be there, repeat the x-ray with the needle
placed into the disc space to confirm you are at the correct level.
Postoperative Care
1. Longer hospital stay than a standard laminotomy approach as the approach is more extensive.
2. Radicular symptoms postoperatively are more common than standard
laminotomy and take longer to resolve.
3. No immobilization is necessary.
Case Report
A 49-year-old white man presenting with severe radicular pain and some
back pain was referred for possible fusion surgery. He had previously undergone three disc explorations on separate occasions at the L3-L4 and L4L5 levels. MRI and CT discogram showed a far lateral extraforaminal HNP
at the L4-L5 level. Lateral approach revealed a free fragment herniated disc
in the far lateral zone. Its removal resulted in resolution of the patients’
symptoms; no fusion was necessary.
Conclusions
1. The far lateral approach is safe and effective.
2. It is the only way to get there without resection of the pars or facet joint.
3. Postoperative instability is minimal.
4. A high index of suspicion and understanding the location and anatomy of the herniation can lead to the diagnosis.
5. Examine this area on all of your imaging studies. Far lateral HNPs are
not uncommonly missed by surgeons, clinicians, and radiologists.
Suggested Readings
Donaldson WF III, Star MJ, Thorn RP. Surgical treatment for the far lateral
herniated lumbar disc. Spine 1993;18:1263−1267.
Zindrick MR, Whiltse LL, Rausching W. Disc herniations lateral to the in-
travertebral foramen. In: White AH, Rothman RH, Ray CD, eds. Lumbar
Spine Surgery. St. Louis: CV Mosby; 1987:195–207.
Eurostile
44 FAR LATERAL DISCECTOMY
205
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Figure 44–1
Magnetic resonance imaging (MRI) cross section.
Figure 44–2
Sagittal MRI view at the level of the pedicle. Note disc herniation going out
and upward, compressing the nerve root into the pedicle above.
Figure 44–3
Computed tomography (CT) discogram confirming that the herniation is
contiguous with the disc space.
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206
SECTION III THE LUMBAR SPINE
Eurostile
L2
L3
L4
L5
L4
Pedicle
Spinal
nerve
root
Herniated
disc
L4-L5
Disc
Skin
incision
L3
L4
L5
A
Figure 44–4
(A) Midline skin incision, fascial incision 1.5 cm lateral. (B) Enter the interval between the muscle
bellies to the level of the facet joint.
B
L3
L 4 pedicle
Pedicle
(dotted
circle)
Spinal
nerve
root
Herniated
disc
A
L4
Spinal nerve
root pushed
superiorly
Herniated disc
L4-L5
Transverse
process
Rongeur
(micro)
L5
Foraminotomy
Figure 44–5
(A) View of the L4-L5 lateral extraforaminal area through the paraspinal approach. Retractors in place; muscle elevated off the transverse
processes. (B) After removal of the intertransverse ligament the nerve root is visible. Partial resection of the lateral facet joint to facilitate visualization of the disc space.
Eurostile
44 FAR LATERAL DISCECTOMY
B
207
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45
En-Bloc (“Trap-Door”) Laminectomy
of the Lumbar Spine
Avi J. Bernstein and David Lee Spencer
Goals of Surgical Treatment
To achieve a lumbar laminectomy using a straightforward, efficient, and reproducible technique that provides a safer and more effective exposure of
the central spinal canal with easy access to the lateral recess and foramina.
Diagnosis
Lumbar spinal stenosis, lateral recess stenosis, and foraminal stenosis are
all diagnosed with advanced radiographic means. The diagnosis may be
considered based on clinical symptoms of neurogenic claudication or
radiculopathy; the confirmation, however, is based on computed tomography (CT) scanning, CT myelography, or magnetic resonance imaging (MRI)
scanning. It is our opinion that even though highly sophisticated, well-performed MRI scans can provide a radiographic diagnosis of spinal stenosis,
CT myelography remains the gold standard and is a truer representation of
the severity and extent of the underlying pathology. In addition the lateral
recesses and foramina are better visualized with postmyelographic CT
scans than plain CT or MRI scanning.
Preoperative symptoms of neurogenic claudication, as distinguished
from vascular claudication, are pathognomonic for spinal stenosis. Walking distances are diminished, symptoms are aggravated by standing and
walking and relieved by sitting or forward flexion of the spine, and symptoms generally radiate from the buttocks into the posterior thighs and into
the calves, either bilaterally or unilaterally. The neurologic examination is
commonly normal, but some patients are noted to walk in a forward flexed
fashion with extension maneuvers aggravating their symptoms. X-rays
commonly reveal spondylosis or spondylolisthesis; however, even normal-appearing x-rays with minimal degenerative change may underestimate the degree of spinal stenosis, because stenosis commonly results from
secondary soft tissue changes such as disc bulging, disc herniation, facet
synovial hypertrophy, and buckling of the ligamentum flavum. Secondary
degenerative hypertrophic facet changes and instability including spondylolisthesis suggest subarticular lateral recess stenosis and foraminal stenosis.
In performing lumbar myelography, it is important to obtain weight-
bearing anteroposterior (AP), lateral, and oblique views, as they will demonstrate the functional pathology that is symptomatic in the upright
position. Absence of these views may completely miss the diagnosis.
Indications for Surgery
1. Symptomatic spinal stenosis, lateral recess stenosis, or radiculopathy
unrelievable through symptomatic means.
2. Any indication for routine lumbar laminectomy where access to the
central spinal canal, lateral recesses, or foramina are required as part of
an open procedure.
3. Laminectomy performed in combination with posterior spinal fusion
as a source of additional bone graft and to assist in pedicle evaluation.
Contraindications
1. Prior limited laminectomy or partial laminectomy with secondary scar
formation and potential dural adhesions. Under these circumstances
extreme caution must be applied to ensure that adhesions do not result
in dural laceration.
2. Unidentifiable anatomy.
Advantages
1. Improved procedural time
2. Lower risk and rate of dural laceration
3. Reduction of blood loss
Disadvantage
Iatrogenic instability due to excessive facet resection.
Procedure
We refer to en-bloc laminectomy as “trap-door” laminectomy, evoking the
notion that the lamina and spinous process are removed as a single unit in
a swift and safe fashion. Once the spine is subperiosteally exposed through
a midline incision out to the level of the facet joints, retractors are placed,
and the appropriate levels for resection are determined radiographically.
The operation is achieved with basic surgical instruments. A one-quarterinch osteotome or chisel, a large blunt nose Leksell rongeur, and a 3-mm or
4-mm, 45-degree angled Kerrison punch are critical to performing this
technique (Fig. 45–1).
The interspinous ligaments are resected. Inferior facet osteotomy is performed, using an osteotome or chisel, ensuring that less than one third of
the facet is removed (Fig. 45–2). This maneuver allows access to the lamina
for the Leksell rongeur. The osteotome cut is directed toward the superior
facet to avoid canal penetration and is surprisingly safe. The facets are resected at the level of laminectomy and one level cephalad. Multiple-level
laminectomies are done in the same fashion, resecting the facets at each
level and one level cephalad. The interspinous ligament is resected only at
the most cephalad and most caudal levels. Next the lamina is thinned with
a large, double-action Leksell rongeur to the deep cortex (Fig. 45–3). The
broad nose of the rongeur allows this to be done safely. Very hard bone may
be thinned using a power burr, but requires extreme caution. Inadequate
thinning of lamina can make for hard going with the Kerrison punch. Next
the Kerrison punch completes the laminotomy from a caudal to cephalad
direction (Fig. 45–4). The laminotomy is placed laterally in the canal, just
medial to the pedicle. The tip of the Kerrison is swept to dissect dura from
the overlying bone, and the “punch” is made either directly cephalad or
slightly lateral, minimizing risk of dural laceration (Fig. 45–5).
Once the bilateral laminotomies are complete, the spinous process and
remaining lamina is loosely attached to the spine by the ligamentum
flavum. The spinous process may be “wiggled” to ensure that the laminotomies are complete. The bone is then easily removed by grasping the
spinous process with a clamp and gently dissecting the ligamentum
flavum with a large blunt curet. The dura easily separates from the lamina,
and the rare adhesion can be further dissected under direct vision (Fig. 45–
6). The procedure is completed by performing lateral recess decompression using the Kerrison (Figs. 45–7 and 45–8). Foraminotomies and discotomies are completed at this time. In the case of fusion, the lamina bone
is morcelized and added to the other bone graft.
Pitfalls
It is important when performing this technique to be respectful of the facet
joints. Spinal instability increases when more than 50% of the facet is removed bilaterally, in cases where laminectomy is done without fusion. A
conservative osteotome cut should be performed over the inferior third of
the facet to avoid excessive facetal resection. In addition, it is helpful to
take the Leksell rongeur bites medial enough to retain the lateral aspect of
the superior articular facet.
Another potential pitfall is the osteotome’s penetrating into the spinal
canal. This can easily be avoided by ensuring that the direction of the
osteotome is slightly lateral so that it runs into the supraarticular facet,
completing the inferior facetectomy of the inferior articular facet. Any
bleeding that may occur after the lamina is removed may be easily controlled with Gelfoam or bipolar cautery and, in some cases, bone wax on
the exposed bony surfaces.
We recommend that this procedure is first performed on patients who
are undergoing concomitant fusion so that experience can be gained in optimal facetal resection, which is of less consequence in those patients undergoing fusion. Make sure that the exposure is carried out to the lateral
aspect of the facet joint at the level of resection, as well as the level
cephalad so that the facet joints can be easily observed for osteotomy. Pulling up on the spinous process with a Kocher clamp will help visualize the
inferior articular facet for osteotomy.
Complications of Instrumentation
1. The most concerning intraoperative complication with any
laminectomy procedure is dural laceration. If this should occur, it
should be addressed and repaired when possible and may be reinforced with fibrin glue.
2. The other potential complication is postoperative instability that
would be demonstrated on follow up x-rays in patients with persistent
or recurrent complaints. The incidence of these complications should
be quite low.
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208
SECTION III THE LUMBAR SPINE
Eurostile
One third of
interior facet
removed
L2
L3
L4
L5
Figure 45–1
Basic instruments required to perform en-bloc laminectomy.
Thin lamina with large, double-action Leksell
rongeur to the deep cortex
Figure 45–2
The inferior facet osteotomy is performed with an osteotome, removing less than
one third of the inferior facet.
Rongeur
Figure 45–3
The lamina is thinned using a double-action Leksell rongeur down to the deep
cortex, no wider than the width of the rongeur.
Eurostile
45 EN-BLOC (“TRAP-DOOR”) LAMINECTOMY OF THE LUMBAR SPINE
Complete
laminotomy
from candal to
cephalad with
Kerrison punch
Punch
Figure 45–4
A Kerrison rongeur is used to complete the osteotomy of the lamina bilaterally.
209
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